Two stroke cycle internal combustion engines

ABSTRACT

A multi cylinder two stroke cycle internal combustion engine of known construction having an individual crankcase compartment for each cylinder 11 formed in a crankcase 12, the crankcase 12 including a wall 25,25 separating two adjacent crankcase compartments. A crankshaft 13 extends through the wall 25,26 with a journal 29 thereof supported in a bearing assembly 30 has an outer bearing ring 32 non-rotatably mounted in the wall 25,26. The outer bearing ring 32 has an axial extent greater than the thickness of the wall 25,26 to provide an internal annular surface co-axial with a shoulder 36 on the crankshaft that presents an opposing external annular surface to the internal annular surface of the bearing ring 32. A fluid seal is provided between the internal and external annular surfaces to prevent the passage of gas between the crankcase cavities.

BACKGROUND OF THE INVENTION

This invention relates to the construction of the crankshaft andcylinder block of a two stroke cycle internal combustion engine toprevent the passage of charge air between the respective crankcasecompartments of adjacent cylinders of the engine.

Engines operating on the conventional two stroke cycle require theincoming air charge to the cylinders of the engine to be compressed toan above atmospheric pressure in order that the air charge will flowinto the engine cylinder while the exhaust gas from the previous cycleis being discharged. There are two basic modes of providing the requireddegree of compression of the charge gas, one being to provide acompressor (supercharger) and the other to effect compression of thecharge air in the engine crankcase by the downward movement of thepiston during the exhaust stroke. Engines employing the latter procedurefor compressing the air charge are commonly referred to as crankcasecompression two stroke cycle engines and require the crankcase to beeffectively sealed in order to achieve the required degree ofcompression of the air charge to be generated by the movement of thepiston during the exhaust stroke. Accordingly, in a multi cylinder twostroke cycle engine operating on the crankcase compression systemrequires an individually sealed crankcase compartment to be provided foreach cylinder of the engine.

Another characteristic of two stroke cycle engines operating on thecrankcase compression system is that the crankcase can not be used as areservoir for lubricating oil, and oil from a pressure circuitrylubrication system can not be permitted to be directly delivered intothe crankcase. Accordingly, the crankshaft and connecting rod bearingscan not normally be of the conventional plain metal type, and areusually of the anti friction type such as ball or roller bearings, whichcan effectively operate with minimal lubrication. As such bearings donot form a seal between adjacent crankcase compartments as is providedby a plain metal bearing, provision must be made to obtain an effectiveseal between the cylinder block and crankshaft journals, where thecrankshaft passes through the dividing wall between adjacent crankcasecompartments of a multi two stroke cycle cylinder engine, to prevent thepassage of charge air from one to the other through the anti-fractionbearing.

The need to provide both a bearing and a seal within the wall separatingadjacent crankcase compartments normally requires the centre distancebetween adjacent cylinders to be increased so that the dividing wall isof sufficient width to accommodate the axial length of the ball orroller bearing together with the axial length of an appropriate sealstructure. This results in an increase in the centre distance ofadjacent cylinders which is contrary to the requirement of minimisingthe axial length of multi cylinder engines to reduce the total weightthereof, to reduce the torsional vibration in the crankshaft, and toreduce the space requirement of the engine compartment of a vehicle,thus contributing to overall reduction in weight of the vehicle, and thedrag co-efficient of the vehicle body.

The above problem has led to a proposed constructions wherein the centredistance between the cylinder can be reduced and the required bearingand seal support is provided by increasing the width of the wall belowthe level of the cylinders. However, this construction gives rise topotential problems in manufacture as the portion of the wall having theincreased width can laterally project into a location below the bore ofthe cylinders on one or both sides of the wall. This lateral projectionof the wall to below the cylinder can interfere with the machining ofthe bore of the cylinders and the assembling of the piston into thecylinder. Both of these operations are preferably performed from thecrankcase end of the cylinders for accuracy and convenienceconsideration.

SUMMARY OF THE INVENTION

It is therefore the object of the present invention to provide aconstruction of a multi cylinder two stroke cycle engine wherein thebearing and adjacent seal in the wall between adjacent crankcasecavities is constructed so as to minimise the required axial spacing ofthe cylinders associated with the respective crankcase cavities.

With this object in view there is provided a multi-cylinder two strokecycle reciprocating internal combustion engine, said engine including acylinder block incorporating a plurality of cylinders, a crankshaft, acrankcase detachably secured to the cylinder to define an individualcrankcase compartment to communicate with each cylinder, said crankcasecompartments being separated from one another by respective internalwalls, each internal wall supporting a bearing assembly to rotatablysupport the crankshaft, said walls being split in a common planediametral to the crankshaft axis, whereby a first part of each wall isintegral with the cylinder block and a second part is integral with thecrankcase, each said bearing assembly including an outer bearing ringnon-rotatably mounted in the respective internal wall co-axial with theaxis of the crankshaft, said first pad of each wall being configured soas not to extend into the area defined by an imaginary extension of theinternal surface of the cylinder on at least one side of said wall, andthe outer bearing ring mounted therein having an axial extent to projectinto said area on at least one side of the wall.

Preferably the first part of the wall is configured so as to not extendinto the area defined by the imaginary extension of the respectivecylinders of each side of the first part of the wall. Further in such aconstruction the bearing ring preferably extends beyond the first partof the wall on each side thereof.

Conveniently the bearing ring is of sufficient length in the axialdirection to provide for seal means to be operatively interposed betweenthe bearing ring and the crankshaft in addition to providing the bearingsupport for the crankshaft.

It will be appreciated that as the crankcase is a separate componentfrom the cylinder block, and is usually removed therefrom duringmachining of the cylinder block and the assembly of the pistons thereto,the width of the second portion of the wall, forming part of thecrankcase can be of the same width as the bearing ring. It is preferablefor the second portion of the wall to be of the same width as thebearing ring to provide additional support for the bearing assembly andrigidity of the crankshaft support.

In accordance with another aspect of the invention there is provided amulti cylinder two stroke cycle internal combustion engine having anindividual crankcase compartment for each cylinder formed in acrankcase, said crankcase including a wall separating two adjacentcrankcase compartment, a crankshaft extending through said wall with ajournal of said crankshaft supported in a bearing assembly mounted insaid wall, said bearing assembly having an outer bearing ringnon-rotatably mounted in said wall with the outer surface of the bearingring in sealed relation to said wall, said outer bearing ring having anaxial extent greater than the thickness of that portion of the wall onthe cylinder Side of the crankshaft axis to provide an internal annularsurface co-axial with said crankshaft journal, and a shoulder on thecrankshaft located to present an opposing co-axial external annularsurface to said internal annular surface, and seal means operativebetween said internal and external annular surfaces to provide a sealbetween the adjacent crankcase compartments.

Conveniently the seal means is a seal ring engaging the outer bearingring in a substantially non-rotational sealing relation and projectinginto a peripheral groove in the crankshaft with close running clearanceto provide a seal in the known manner. In operation, a film of theengine lubricant: will be established between the seal ring and theopposing surfaces of the groove in the crankshaft to create ahydrodynamic form of lubrication therebetween.

Alternatively a labyrinth type seal configuration can be providedbetween the respective annular surfaces on the crankshaft and thebearing outer ring.

The above construction permits the seal means to overhang the cylinderbore of the engine associated with the crankcase compartment, withinwhich the seal means is located, without portion of the actual wall ofthe crankcase compartment overhanging the cylinder bore. Thus the axialspacing between adjacent cylinder bores in the cylinder block may bereduced by the extent that the seal means overhang the cylinder bore,without such overhang interfering with the convenient machining of thecylinder bores and/or assembly of the pistons thereto.

The invention will be more readily understood from the followingdescription of one practical arrangement of a three cylinder two strokecycle engine incorporating the two embodiments of the seal arrangementas proposed by the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a longitudinal sectional view along the plane of the axis ofthe crankshaft of the engine;

FIG. 2 is a sectional view along the line 2--2 in FIG. 1;

FIG. 3 is an enlarged view of the area A ion FIG. 1;

FIG. 4 is a view similar to FIG. 3 of an alternative seal means.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to FIG. 1 of the drawings, the engine comprises a cylinderblock 10 having three parallel in line cylinder bores 11 formed therein,a detachable crankcase 12 and a one piece crankshaft 13. An enginecylinder head is normally fitted to the top face of the cylinder blockbut is omitted from the drawings of this specification.

The crankcase 12 and cylinder block 10 have abutting surfaces which lieon the axial plane of the crankshaft 13 at right angles to the axes ofthe cylinder bores 11 as seen at 14 in FIG. 2. The respective front andrear journals 15 and 16 of the crankshaft are supported in respectivebearings 17 and 18 with outboard oil seals 19 and 20 of conventionalconstruction.

Each of the connecting; rods 21 are connected in the conventional mannerto the respective pistons 22 and to the respective eccentric crankpins23 of the crankshaft 13. Conventional split roller bearings 24 areprovided between the connecting rod and the crankpin as is customary intwo stroke cycle engines.

The crankcase 12 has formed therein two spaced internal transverse lowerwalls 25 which abut corresponding transverse upper walls 26 formed inthe lower part of the cylinder block 10. The abutting lower and upperwalls 25 and 26 divide the space defined by the cylinder block 10 andcrankcase 12 in three crankcase compartments each communicating with arespective cylinder bore. Each of the abutting walls 25,26 also define abearing bore 27, in axial alignment with front and rear crankshaftbearings 17 and 18, receiving the respective roller bearing assemblies30. Each of the roller bearing assemblies 30 are of the known split typeso that they may be assembled about the respective intermediate journals29 of the crankshaft 13.

The two sections of the split roller bearing assemblies 30 are held inthe desired assembled relationship by being clamped between thecrankcase wall 25 and cylinder block wall 26 so that the Outer race 32of the bearing assembly 30 is held against rotation. In addition alocating dowell 31 is provided to be received in respective alignedapertures in the cylinder block and outer race 32 of the bearingassembly.

As can be clearly seen in FIGS. 3 and 4, the cylinder block wall 26 issubstantially narrower than the complementary crankcase wall 25. Thecylinder block wall 26 has a thickness equal to the thickness of thewall between the cylinder bore 11 measured at the longitudinal axis ofthe cylinder block. Accordingly the cylinder block wall 25 does notextend at any point into a location immediately below the cylinder bore11 thus providing unobstructed entry of a piston into the cylinder borefrom the lower or crankcase side of the cylinder block 10. In contrast,the crankcase wall 25 is of a substantially greater thickness andextends below each of the cylinder bores 11 on either side of the wall.

The outer race 32 of each bearing assembly 30 has a greater axial lengththan the cylinder block wall 26, and thus projects from either sidethereof, and is substantially equal to the width of the crankcase wall25.

The outer race 32 also has a greater axial length than the intermediatejournal 29 of the crankshaft and of the rollers 28 of the bearingassembly 30, which are substantially the same length as the intermediatejournals 29. As seen in FIGS. 1 and 3, the rollers 28 are offset withrespect to the outer races 32 and the walls 25,26 respectively, so thatthe spigot 35 formed as part of the crankshaft 13 may extend co-axiallyinto the outer race 32. Thus the rollers 28 of the bearing assembliesare located axially between the shoulder 36 of the crankshaft and theface 37 of the spigot 35.

As seen more clearly in FIG. 3, each spigot 31 is provided with aplurality of co-axial parallel grooves 38 in the peripheral surfacethereof with the peripheral surface of the ridges 39 between saidgrooves in close running relationship with the internal face of theouter race 32 of the bearing assembly. This configuration forms aconventional labyrinth type seal to substantially prevent the transferof air from one crankcase compartment to the adjoining compartment.

It will be noted that the outer race 32 of the bearing assembly 30projects beyond the wall 26 of the adjacent cylinder bore 11 so as tolie in the line of the piston as it reciprocates in the bore. However,as the outer race is not in position within the cylinder block duringthe machining thereof, nor during the introduction of a piston in thecylinder bore during assembly, the outer race does not interfere withthe free passage of the various tools, through the cylinder bore, suchas are required in the forming and honing of the cylinder bores.

This construction enables the centre distance between the cylinder boresto be reduced without necessitating a similar reduction in the axiallength of the combined bearing and seal areas of the intermediatebearings supporting the crankshaft.

In the above description, reference has been made to roller bearingassemblies supporting the crankshaft, however, it is to be understoodthat other forms of anti-friction bearing may be used, including ballbearings. In some engines the bearing may be of the plain slipperbearing type commonly used in engines. Also other types of sealconstruction may be used as an alternative to a labyrinth seal. One formof alternative seal means would be a single split outwardly expandingring similar to a conventional piston ring as is shown in FIG. 4.

in this construction a peripheral groove 40 is provided in the spigot 35on the crankshaft 13 at a location to be positioned within the outerbearing race 32 when assembled. The seal ring 41 is of a split outwardlyexpanding type so that it must be compressed from its free diametralsize to be received in the outer bearing race 32, as in the manner of apiston ring. The seal ring 41 is of an axial length to be received inthe peripheral groove 40 with a controlled clearance between the wallsof the groove and the diametral faces of the seal ring, so thathydrodynamic lubrication conditions will exist therebetween when thecrankshaft is rotating and the seal ring 41 is stationary with the outerbearing race 32.

A further form of seal that can be used between the crankshaft spigot 35and the outer bearing race 32 is a convention flexible seal as commonlyused in conjunction with a rotating shaft or member and as generallyshown diagrammatically at 19 and 20 in FIG. 1.

The claims defining the invention are as follows:
 1. A multi-cylindertwo stroke cycle reciprocating internal combustion engine, said engineincluding a cylinder block incorporating a plurality of cylinders, acrankshaft, a crankcase detachably secured to the cylinder block todefine an individual crankcase compartment communicating with eachcylinder, said crankcase compartments being separated from one anotherby respective internal walls, each internal wall supporting a bearingassembly to rotatably support the crankshaft, said walls being splitacross the crankshaft axis, whereby a first part of each wall isintegral with the cylinder block and a second part is integral with thecrankcase, each said bearing assembly including an outer bearing ringnon-rotatably mounted in the respective internal wall co-axial with theaxis of the crankshaft, said first part of each wall being configured soas not to extend into the area defined by an imaginary extension of theinternal surface of the cylinder on at least one side of said wall, andthe outer bearing ring mounted therein having an axial extent to projectinto said area on at least one side of the wall, wherein a seal means isoperatively interposed between a part of the outer bearing ring and thecrankshaft at a location where the bearing ring extends beyond the firstpart of the wall to provide a seal between adjacent crankcasecompartments and wherein a bearing means is operatively interposedbetween the outer bearing ring and the crankshaft, the seal means beinglocated directly on the crankshaft one side of the bearing means.
 2. Anengine as claimed in claim 1 wherein the first part of the wall isconfigured so as to not extend into the area defined by the imaginaryextension of the respective cylinders on each side of the first part ofthe wall.
 3. An engine as claimed in claim 2, wherein the outer bearingring extends beyond the first part of the wall on each side thereof. 4.An engine as claimed in claim 3, wherein the second part of the wall isof a width substantially the same as the outer bearing ring.
 5. Anengine as claimed in claim 2, wherein the second part of the wall is ofa width substantially the same as the outer bearing ring.
 6. An engineas claimed in claim 1, wherein the second part of the wall is of a widthsubstantially the same as the outer bearing ring.
 7. An engine asclaimed in claim 6 wherein the seal means is a resiliently compressiblering located substantially stationary in a compressed condition in thebearing ring, said seal ring extending into an externally open groove inthe crankshaft and adapted to establish a fluid seal therewith as thecrankshaft rotates.
 8. An engine as claimed in claim 1 wherein a bearingmeans is operatively interposed between the outer bearing ring and thecrankshaft, the bearing means being offset with respect to the saidouter bearing ring to provide clearance for the seal means.
 9. An engineas claimed in claim 8 wherein the crankshaft includes a crankshaftjournal supported in the bearing assembly, the crankshaft journal beingoffset with respect to the outer bearing ring.
 10. An engine as claimedin claim 8 wherein the seal means is a resiliently compressible ringlocated substantially stationary in a compressed condition in thebearing ring, said seal ring extending into an externally open groove inthe crankshaft and adapted to establish a fluid seal therewith as thecrankshaft rotates.
 11. An engine as claimed in claim 1 wherein thecrankshaft includes a crankshaft journal supported in the bearingassembly, the crankshaft journal having an axial extent less than theaxial extent of the outer bearing ring.
 12. A multi-cylinder two strokecycle internal combustion engine having an individual crankcasecompartment for each cylinder formed in a crankcase, said crankcaseincluding a wall separating two adjacent crankcase compartments, acrankshaft extending through said wall with a journal of said crankshaftsupported in a bearing assembly mounted in said wall, said bearingassembly having an outer bearing ring non-rotatably mounted in said wallwith the outer surface of the bearing ring in sealed relation to saidwall, said outer bearing ring having an axial extent greater than thethickness of that portion of the wall on the cylinder side of thecrankshaft axis so that at least part of the bearing ring extends beyondthe portion of the wall, the outer bearing ring providing an internalannular surface co-axial with said crankshaft journal, the crankshaftpresenting an opposing co-axial external annular surface to saidinternal annular surface, and seal means operative between said internaland external annular surfaces to provide a seal between the adjacentcrankcase compartments, wherein said seal means is located in thatportion of the bearing ring that extends beyond the said portion of thewall and wherein a bearing means is operatively interposed between theinternal and external surfaces, the seal means being located directly onthe crankshaft to one side of the bearing means.
 13. An engine asclaimed in claim 12 wherein the crankcase is formed by a portion of acylinder block and a crankcase portion detachably secured to saidcylinder block, said cylinder block and crankcase portion each having apart thereof adapted to cooperate to form said wall to separate the twoadjacent crankcase compartments when the cylinder block and crankcaseportion are secured together.
 14. An engine as claimed in claim 13wherein the seal means is a resiliently compressible ring locatedsubstantially stationary in a compressed condition in the bearing ring,said seal ring extending into an externally open groove in thecrankshaft and adapted to establish a fluid seal therewith as thecrankshaft rotates.
 15. An engine as claimed in claim 12 wherein theseal means is a resiliently compressible ring located substantiallystationary in a compressed condition in the bearing ring, said seal ringextending into an externally open groove in the crankshaft and adaptedto establish a fluid seal therewith as the crankshaft rotates.
 16. Anengine as claimed in claim 12 wherein a bearing means is operativelyinterposed between the internal and external annular surfaces, thebearing means being offset with respect to the internal annular surfaceto provide clearance for the seal means.
 17. An engine as claimed inclaim 16 wherein the crankshaft journal is offset with respect to theouter bearing ring.
 18. An engine as claimed in claim 16 wherein theseal means is a resiliently compressible ring located substantiallystationary in a compressed condition in the bearing ring, said seal ringextending into an externally open groove in the crankshaft and adaptedto establish a fluid seal therewith as the crankshaft rotates.
 19. Anengine as claimed in claim 12 wherein the crankshaft journal has anaxial extent less than the axial extent of the outer bearing ring.
 20. Amulti-cylinder two stroke cycle reciprocating internal combustionengine, said engine including a cylinder block incorporating a pluralityof cylinders, a crankshaft, a crankcase detachably secured to thecylinder block to define an individual crankcase compartmentcommunicating with each cylinder, said crankcase compartments beingseparated from one another by respective internal walls, each internalwall supporting a bearing assembly to rotatably support the crankshaft,said walls being split across the crankshaft axis, whereby a first partof each wall is integral with the cylinder block and a second part isintegral with the crankcase, each said bearing assembly including anouter bearing ring non-rotatably mounted in the respective internal wallco-axial with the axis of the crankshaft, said first part of each wallbeing configured so as not to extend into the area defined by animaginary extension of the internal surface of the cylinder on at leastone side of said wall, and the outer bearing ring mounted therein havingan axial extent to project into said area on at least one side of thewall, wherein a seal means is operatively interposed between a part ofthe outer bearing ring and the crankshaft at a location where thebearing ring extends beyond the first part of the wall to provide a sealbetween adjacent crankcase compartments the seal means being positionedbetween the bearing assembly and the crankshaft, and being positioneddirectly on the crankshaft radially offset from the radial center pointof the bearing assembly.
 21. A multi-cylinder two stroke cycle internalcombustion engine having an individual crankcase compartment for eachcylinder formed in a crankcase, said crankcase including a wallseparating two adjacent crankcase compartments, a crankshaft extendingthrough said wall with a journal of said crankshaft supported in abearing assembly mounted in said wall, said bearing assembly having anouter bearing ring non-rotatably mounted in said wall with the outersurface of the bearing ring in sealed relation to said wall, said outerbearing ring having an axial extent greater than the thickness of thatportion of the wall on the cylinder side of the crankshaft axis so thatat least part of the bearing ring extends beyond the portion of thewall, the outer bearing ring providing an internal annular surfaceco-axial with said crankshaft journal, the crankshaft presenting anopposing co-axial external annular surface to said internal annularsurface, and seal means operative between said internal and externalannular surfaces to provide a seal between the adjacent crankcasecompartments, wherein said seal means is located in that portion of thebearing ring that extends beyond the said portion of the wall, the sealmeans being positioned between the bearing assembly and the crankshaft,and being positioned directly on the crankshaft radially offset from theradial center point of the bearing assembly.